1. Field of the Invention
The present invention relates to an apparatus for and a method of processing an object to be processed, and, more particularly, to an apparatus for and a method of processing an object to be processed while restricting shading damages.
2. Description of the Related Art
Of reactive ion etching apparatuses, there is included a magnetron reactive ion etching apparatus, which efficiently performs etching processing with a magnetic field generated from a magnetron.
Etching processing using a magnetron reactive ion etching apparatus is performed as follows: First, high-frequency electric power is supplied to a pair of electrodes arranged inside a processing container of the magnetron reactive ion etching apparatus so as to form an electric field. Next, electrons are discharged from an etching gas, thereby to form a plasma at the periphery of the surface of an object to be processed, such as a semiconductor wafer or the like, arranged on the electrodes. Then, a magnetic field is formed in a horizontal direction with respect to the semiconductor wafer using magnetic field formation means, for example, a permanent magnet or the like. In doing this, the electrons are caused to be in cyclotron motion (spiral motion), whereby the frequency at which the electrons and neutral particles collide with each other is high. Under this structure where the electrons and the neutral particles collide with each other, a reactive gas is efficiently ionized at the periphery of the surface of the semiconductor wafer. The ions are injected into the processing surface of the semiconductor wafer, thus etching is efficiently performed as a result of both a sputtering effect and a chemical reaction of ions.
In thus structured magnetron reactive ion etching apparatus, it is important that a magnetic field is uniformly formed in a horizontal direction with respect to the semiconductor wafer. This is because if a magnetic field is not formed uniformly in the horizontal direction, the surface of the semiconductor wafer is etched at a variety of etching speeds. FIG. 10 illustrates a dipole ring magnet as magnetic field formation means used in the magnetron reactive ion etching apparatus.
As illustrated in FIG. 10, a dipole ring magnet 101 comprises a dipole ring body 102 formed in a ring-like shape and a plurality of anisotropic segment cylindrical magnets 103 arranged in the dipole ring body 102 at equal intervals. The anisotropic segment cylindrical magnets 103 are arranged in such a way that their magnetization directions are slightly differently oriented from one another, so as to form a magnetic field totally in one direction.
The dipole ring magnet 101 is arranged outside a processing container 104, and a magnetic field B is formed in a horizontal direction with respect to a semiconductor wafer 105.
The dipole ring magnet 101 can rotate along its circumferential direction. In rotating this dipole ring magnet 101, a rotational magnetic field is formed uniformly in a horizontal direction with respect to the semiconductor wafer 105, and the density of a plasma on the semiconductor wafer 105 can uniformly be made.
The magnetic field strength is large in magnetron reactive ion etching, thus a problem is that shading damage is likely to occur in an over-etching process, for example. For the sake of easy description of shading damage, FIG. 11 illustrates an exemplary diagram of a transistor in an over-etching process.
As illustrated in FIG. 11, a transistor 111 is a MOS type transistor wherein a gate oxide film 113 and a gate electrode 114 are formed on a semiconductor wafer 112. The first interlayer insulating film 115 is formed on a corresponding part of the semiconductor wafer 112 on which the gate oxide film 113 and the gate electrode 114 are not formed. Metal wiring 116 is formed on the first interlayer insulating film 115 and the gate electrode 114. The second interlayer insulating film 117 is formed on the metal wiring 116, and a resist 118 is arranged on the second interlayer insulating film 117. By performing a magnetron reactive ion etching process, some part of the second interlayer insulating film 117 which is not masked by the resist 118 is etched, resulting in forming a hole 119.
During the magnetron reactive ion etching process, electrons are attracted (being in cyclotron motion) to a magnetic field. The speed (the speed of the electrons travelling in a top-down direction, as illustrated in FIG. 11) at which the electrons move toward the hole 119 is low, thus the electrons are hardly to enter the hole 119. As compared to the electrons, positive charge ions are unlikely to be attracted to the magnetic field for some reasons that their mass is great and the like. Hence, the speed at which positive ions move toward the hole 119 is higher than the speed of electrons travelling to the hole 119, and the positive ions are likely to enter the hole 119. As shown in FIG. 11, electrons 121 are likely to be charged up on the resist 118 during the over-etching process, while positive ions 120 are likely to be charged up on the bottom of the hole 119. As a result of this, a potential difference occurs in the upper and lower surfaces of the gate insulating film 113. In addition, a current flows through the gate insulating film 113 in a direction shown with an arrow 122 in the drawing, resulting in shading damage in which the gate insulating film 113 is deteriorated.
As a method for preventing such an insulating film from being deteriorated, proposed in Unexamined Japanese Patent Application KOKAI Publication No. H5-308055 is a method for forming gate electrode wiring without deterioration of a gate oxide film. This formation of the gate electrode wiring is achieved by performing magnetic field high-density plasma etching when patterning metal wiring connected to a gate electrode, and performing non-magnetic field low-density plasma etching and patterning the metal wiring before the metal wiring is completely isolated therefrom.
According to this invention, it is possible that an insulating film is prevented from being deteriorated as a result of shading damage, etc., since changing from the magnetic field high-density plasma etching to the non-magnetic field low-density plasma etching can prevent electrons from being attracted to the magnetic field.
However, the etching speed dramatically decreases if the magnetic field high-density plasma etching is changed to the non-magnetic field low-density plasma etching. Therefore, if the magnetic field high-density plasma etching is not performed until just before the etching process is completed, the essential purpose of the magnetron reactive ion etching for efficiently performing an etching process is not realized.
On the contrary, if the magnetic field high-density plasma etching is performed until just before the etching process is completed, the gate oxide film is exposed from a part of a hole, which is made as a result of the etching. In the structure where the gate oxide film is thus exposed, the electrons are distributed not uniformly on the semiconductor wafer, bringing another problem that charge up damage occurs.
The present invention has been made in consideration of the above problems. It is accordingly an object of the present invention to provide an apparatus for and a method of efficiently processing an object to be processed while restricting shading damages.
In order to accomplish the above object, according to the first aspect of the present invention, there is provided a processing apparatus, comprising:
a processing container;
an electrode unit which is arranged inside said processing container and includes a first electrode and a second electrode facing each other via an object to be processed;
a processing gas supply section which supplies a processing gas into said processing container;
a gas exhaust section which exhausts said processing container of a gas;
an electric field formation section which supplies high-frequency electric power to said electrode unit and forms an electric field between the first electrode and the second electrode;
a magnetic field formation section which forms a first magnetic field state, including a magnetic field in said electrode unit in a direction perpendicular to the direction of the electric field or in a direction parallel to the object, and a second magnetic field state, including a magnetic field whose magnetic field strength at a periphery of a surface of the object is so satisfactory that an electron Larmor radius is larger than a mean free path of electrons in the magnetic field; and
a magnetic field state switching section which switches a magnetic field state from/to the first magnetic field state to/from the second magnetic field state.
In this structure, the first magnetic field state is formed and an efficient etching process, for example, is performed. In the case where shading damage is likely to occur, the second magnetic field state is switched from the first magnetic field state by the magnetic field state switching means so as to perform, for example, an etching process. In the second magnetic field state, there exists a magnetic field wherein an electron Larmor radius is larger than the mean free path of electrons, thus the processing speed does not dramatically decrease. Because the electron Larmor radius is larger than the mean free path of electrons and there is a high percentage of electrons which pass by the magnetic field and are diffused, the electrons are more likely to enter the bottom of a hole on the processing surface. This achieves restriction of shading damages in an object to be processed.
The second magnetic field includes a magnetic field in a direction perpendicular to the direction of the electric field or in a direction parallel to the object. In this structure, the processing speed is unlikely to decrease, thus achieving an efficient etching process, for example.
The processing gas includes a gas having reactive ion species and used for performing magnetron reactive ion processing for the object. In this structure, an etching process is efficiently performed as a result of both a sputtering effect and a chemical reaction of ions.
The magnetic field state switching section includes a switch control mechanism which switches the first magnetic field state to the second magnetic field state at a predetermined timing. This achieves automatic switching of the magnetic field states.
A magnetic field is uniformly formed on the object in the first magnetic field state and in the second magnetic field state. In this structure, a rotational magnetic field is uniformly formed in a horizontal direction with respect to the object to the processed, and the density of a plasma is even at the object.
The magnetic field formation section includes a plurality of electromagnets which are so arranged that said electrode unit is sandwiched therebetween, and said magnetic field state switching section is capable of switching a flow amount of current flowing to the electromagnets from/to a first flow amount to/from a second flow amount; and
the first flow amount of current flows to the electromagnets so as to form the first magnetic field state, and the second flow amount of current flows to the electromagnets so as to form the second magnetic field state. In this structure, the flow amount of current is switched from the first flow amount to the second flow amount, thereby the magnetic field state is switched from the first magnetic field state to the second magnetic field state.
The magnetic field formation section includes a plurality of permanent magnets which are so arranged that the electrode unit is sandwiched therebetween, and said magnetic field state switching section forms the first magnetic field state by arranging the plurality of permanent magnets in dipole arrangement and also the second magnetic field state by changing directions of magnetic poles of the plurality of permanent magnets. In this structure, a large magnetic field can be formed in the first magnetic field state, achieving an efficient etching process, for example.
According to the second aspect of the present invention, there is provided a method of processing an object to be processed, comprising:
an arranging step of arranging the object between a pair of electrodes forming an electrode unit arranged inside a processing container;
a decompressing step of decompressing the processing container at a predetermined pressure level;
a processing gas supplying step of supplying processing gas into the processing container;
an electric field formation step of supplying high-frequency electric power to the electrode unit and forming an electric field between the pair of electrodes;
a magnetic field formation step of forming in the electrode unit a first magnetic field state in a direction perpendicular to a direction of the electric field or in a direction parallel to the object; and
a magnetic field state switching process of switching a magnetic field state from the first magnetic field state to a second magnetic field state, whose magnetic field strength at a periphery of a surface of the object is so satisfactory that an electron Larmor radius in the second magnetic field state is larger than a mean free path of electrons.
In this structure, the first magnetic field state is formed and an efficient etching process, for example, is performed. In the case where the shading damage is likely to occur, the second magnetic field is switched from the first magnetic field state in the magnetic field state switching process, and the etching process is performed. In this second magnetic field stated, there exists a magnetic field wherein the electron Larmor radius is larger than the mean free path of electrons, thus the processing speed does not dramatically decrease. Because the electron Larmor radius is larger than the mean free path of electrons and there is a high percentage of electrons which pass by the magnetic field and are diffused, the electrons are more likely to enter the bottom of a hole on the processing surface. This achieves restriction of shading damages in an object to be processed.
The second magnetic field state having a magnetic field in the direction perpendicular to the direction of the electric field or in the direction parallel to the object is formed. In this structure, the processing speed is unlikely to decrease, thus achieving an efficient etching process, for example.
The processing gas includes a gas having reactive ion species and used for performing magnetron reactive ion processing for the object. In this structure, an etching process is efficiently performed as a result of both a sputtering effect a chemical reaction of ions.
In the magnetic field state switching process, the first magnetic field state is switched to the second magnetic field state at a predetermined timing. This achieves automatic switching of the magnetic field states.
A magnetic field is uniformly formed on the object in the first magnetic field state and the second magnetic field state. In this structure, a rotational magnetic field is uniformly formed in a horizontal direction with respect to the object to the processed, and the density of a plasma is even at the object.